Hexaaquacobalt(II) Bis[(2-Hydroxy-1,3-propanediamine-N,N,N',N'-tetraacetato)cobalt(III)]

The structure of the title complex, [Co(H₂O)₆][Co(C₁₁H₁₄N₂O₉)]₂, is comprised of discrete [Co(Hpdta)]^- anions (H₄hpdta is 2-hydroxy-1,3-propanediamine-N,N,N',N'-tetraacetic acid) and [Co(H₂O)₆]²⁺ cations in a 2:1 molar ratio. The trivalent Co atom in the anion is coordinated by the hexadentate hpdta chelate ligand, with two aminoN atoms [Co-N 1.948 (3) Å] and four O atoms of the four monodentate carboxylato groups [Co-O = 1.869 (2)-1.914 (2) Å] in a distorted octahedral arrangement, whereas the divalent Co atom in the cation is coordinated in an octahedral manner by six aqua ligands [Co-O 2.078 (2)-2.124 (2) Å]. The crystal structure is stabilized by extensive hydrogen bonding. Each aqua ligand forms two donor hydrogen bonds with the carboxyl O atoms from adjacent anions and the hydroxyl group forms a hydrogen bond with an adjacent carboxyl O atom.

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